1. Field of the Invention
The present invention is based upon Japanese patent application no. 09-257901, filed on Sep. 4, 1997, which is hereby incorporated by reference in its entirety.
The present invention relates to a reformer for a fuel cell, which enables responsive and sufficient vaporization of fuel and enables heat input to follow an abrupt load variation. The reformer is equipped with a reforming unit using a reaction system having a partial oxidation reaction and a steam reforming reaction as a reforming reaction. The reformer further comprises a vaporizing device for vaporizing a raw fuel, which uses a mixture of liquid hydrocarbon such as gasoline or alcohol and water, and an atomizing device for atomizing the raw fuel. The vaporized and atomized fuel is supplied to the reforming unit, and a blowing machine supplies air to the reforming unit.
2. Description of the Related Art
As shown in FIG. 7, since it is necessary to raise the responsiveness of hydrogen supply to a fuel cell to changes in load, a conventional fuel cell power plant (Japanese Patent Unexamined Pub. No. Sho. 60-49569) is constructed such that a fuel tank T as a storage means of a reformed gas or hydrogen is provided between a reforming unit K for reforming a raw fuel to produce the reformed gas rich in hydrogen and a power generating unit H of a main unit of the fuel cell, and the reformed gas or hydrogen is directly supplied to the power generating unit H of the fuel cell from the fuel tank T according to the variation of output.
In another conventional fuel cell power generating apparatus (Japanese Patent Unexamined Pub. No. Hei. 3-252062), as shown in FIG. 8, since improving the responsiveness in vaporization of methanol as a raw fuel fed to a reforming unit K is important for improving the responsiveness of a power generating device H of the fuel cell, a vaporizing device is proposed for atomizing the fuel at a nozzle N, as a means of improving heat conductivity in a vaporizing unit C. A heat exchanger E cools down the heat exchange medium so as to maintain the operating temperature of the power generating device H. An atomized raw fuel is blown by the nozzle N to a heat conductive surface in a heat exchanger for evaporation, and the raw fuel forms a thin and uniform layer on the heat conductive surface, so that the performance of heat exchange is improved and the responsiveness in the evaporation amount is raised.
Moreover, an article xe2x80x9cPartial Oxidation Reforming of Methanolxe2x80x9d in which reforming of methanol is carried out by using a partial oxidation reaction was published in xe2x80x9c1996 EPRI/GRI Fuel Cell Workshop on Fuel Call technology and Developmentxe2x80x9d. However, the foregoing conventional fuel cell power plant has problems that, for example, in the case where the fuel cell using methanol as a raw fuel is used for a vehicle, the variation of output is large, so that its storage device becomes large or the responsiveness of vaporization of methanol can not follow the variation.
In the conventional fuel cell power generating apparatus, since raw fuel is sprayed by the nozzle, there is required such a wide surface that an atomized raw fuel is effectively attached to the heat conductive surface. Since heat conduction of a combustion gas is dominant on the heating side of the vaporizer, the performance of heat conduction is much inferior to the inside of the vaporizer. Thus, the conventional apparatus has a disadvantage that the temperature in the vaporizer and at the heat conduction surface is abruptly lowered by the latent heat of evaporation of a large amount of sprayed methanol in response to the abrupt increase of a load, so that sufficient vaporization can not be carried out.
In the foregoing conventional fuel cell power generating apparatus, heat supply to the heat conduction surface requires heat at least equivalent to the evaporation heat of the raw fuel sprayed by the nozzle. Thus, as a system of the fuel cell, a phosphoric acid type or a solid fused-salt type having a high waste-heat temperature becomes a candidate. However, for use in a moving body such as a vehicle, a solid high polymer film type (generally called PEM), which operates at a low temperature and can be made small and light, is advantageous. However, since the waste-heat temperature is 10xc2x0 C. or less in a PEM fuel cell, evaporation by waste heat becomes difficult.
Thus, although the burner waste heat obtained by burning a fuel cell exhaust gas and the like is used for heat supply, a heat shortage is expected. In direct heat supply by a burner exhaust gas, heat conduction is from gas to solid, so that the performance of heat conduction is much lower than that at the evaporation side, and a wide area heat conduction surface is required for sufficient heat supply. In this case, the size of a heat exchanger is increased, and when a heat medium is used for heat supply at a nozzle, an additional heat exchanger is required, so that the system becomes large and is unsuitable for use in a moving body such as a vehicle.
Further, a reforming reaction in the reforming unit becomes an endoergic reaction by only a conventional steam reforming method, so that there is a problem that heat supply from the outside is always necessary, and heat input cannot follow an abrupt load variation.
It is an object of the invention to provide a reformer of a fuel cell which is responsive to abrupt load variations and provides sufficient vaporization of the fuel.
According to a first aspect of the present invention, a reformer for a fuel cell comprises a reforming unit including a reaction system using a partial oxidation reaction and a steam reforming reaction; a vaporizing device for vaporizing a raw fuel using a mixture of liquid hydrocarbon and water, the vaporizing device communicating with the reforming unit so as to supply the vaporized fuel to the reforming unit; an atomizing device for atomizing the raw fuel and communicating with the reforming unit so as to supply the atomized fuel to the reforming unit; and a blowing machine communicating with the reforming unit so as to supply air to the reforming unit.
According to a second aspect of the present invention, the reformer includes control means for controlling the amount of raw fuel supplied by the atomizing device to the reforming unit and the amount of air supplied from the blowing machine in response to the load variation of the fuel cell.
According to a third aspect of the present invention, the vaporizing device receives hydrogen combustion heat of an exhaust gas from the power generating unit, to vaporize the raw fuel.
According to a fourth aspect of the present invention, the blowing machine includes a blower or a compressor, and the atomizing device includes an air assist type nozzle coupled to the blower or the compressor.
According to a fifth aspect of the present invention, the atomizing device includes an ultrasonic pulverizing device using an ultrasonic vibration.
In the foregoing reformer for the fuel cell of the first aspect equipped with the reforming unit using the reaction system composed of partial oxidation reaction and steam reforming reaction as the reforming reaction, the vaporizing device vaporizes the raw fuel using the mixture of liquid hydrocarbon such as gasoline or alcohol and water and supplies the vaporized fuel to the reforming unit. The atomizing device atomizes the raw fuel and supplies the atomized fuel to the reforming unit. The blowing machine supplies air to the reforming unit so that the reforming unit reforms the vaporized and atomized raw fuel into a gas rich in hydrogen. Thus, the reformer has the effect of enabling the responsive and sufficient vaporization.
According to the foregoing second aspect, the reformer enables responsive and sufficient vaporization and enabling the heat input to follow abrupt load variations.
According to the third aspect, heat supply from the outside becomes unnecessary.
According to the fourth and fifth aspects, the reformer atomizes the raw fuel.